The sound art research program developed from applied research into low frequency sound and sensation
perception. I was interested in the way the body processes sensation and the dialogue between the senses.
This section is a reference for discussion of vibration perception within this site. It constitutes the findings of
research undertaken before the commencement of Master of Art studies.
This page covers research findings on vibration and vbro-acoustic perception, including vibration and auditory interactions and vibro-acoustic therapy. It also addresses early vibration floor testing exploring envelope, frequency, crossover, and audience engagement and feedback.
The Master of Art candidature developed
from a Graduate Certificate and preliminary
Masters research at the Spatial Information
Architecture Laboratory (SIAL).
The initial focus was on using floor-based
vibration as a substitute for subwoofer
sound in a nightclub setting, and the noise
reduction benefits this would offer. I later
moved departments to refocus my work on the
creative potential of vibration technology.
This background research included:
The purpose of my research in this area was
to broadly understand aspects of vibration
perception that could inform my approach to
composition and installation.
Vibration perception
The processing capacity of the tactile system
has been explored in detail through research
with an industrial/noise focus, with key
literature broadly distinguishing between finger
transmitted and whole body vibration.1
The ‘loudness scale’ for vibration differs to
that of sound2, i.e. an equal increase in the dB
level of vibration and acoustic signal won’t
lead to the same perceived increase in level
across both senses. The vibration response can
be understood to generally be more ‘linear’
with stimulus increase, whereas
hearing perception is more like a
‘logarithmic’ function (as equated
in the dB scale for sound pressure
and audio signal).
Comparison of airborne with
structural vibration is an emerging
field,3 and research and anecdotes
around low frequency sensation
from soundwaves cannot be
assumed to transfer to tactile/
vibration perception.
Some vibration studies were not directly
relevant to the whole body vibration focus
of my work, such as those of haptic feedback
for fingers or hands or skin effects. However,
I concluded that these could still be relevant
to understanding the way people process and
perceive vibration in a whole body vibration
context.4 For example:
Vibration and auditory interactions
There is substantial frequency-range cross
over between the active range of vibration
and auditory senses, with hearing extending
below 20Hz (with loss of tonal perception), and
vibration ‘effective’ at a range of frequencies,
depending on its source and the type of body
connection (i.e. skin, whole body or finger).
Compared to the auditory sense, the tactile
sense is relatively lacking in sophistication.5
Studies on perception of timing6 7 8 of musical
auditory/tactile events found that:
Vibro-acoustic therapy and tactile systems
Vibro-acoustic therapies offer a range of
positive physiological and psychological effects
that come from vibration stimulation to the
body (usually while listening to music), such
as relaxation to muscles, pain relief, assistance
with brain disorders and injuries, and other
rehabilitation benefits.12
Vibro-acoustic therapy tends to use vibration
that either reproduces the low-frequency
parts of music, or uses pulsed sinusoidal
tones (such as from beat frequencies), in
line with the principle that ‘exposure to soft,
low frequency and non-rhythmic music...
results in physiological responses indicative of
relaxation.’13
Significant levels of high frequencies through a
vibro-acoustic system can lead to undesirable
or distracting acoustic noise.14
When used in a vibro-acoustic system, the
vibration signal needs to be electronically
compressed (dynamics reduction) to
perceptually align to the acoustic information.15
The vibration floor and soundsystem tests
explored how people respond to different
frequencies and intensities of low frequency
sound and vibration.
In each test, audio material was sent as sound
through a large subwoofer and loudspeakers,
and then sent through the vibration floor
instead of the subwoofer.
I interviewed participants about how the sensation experiences differed, their general
observations of the sound and their spatial and
bodily connection to it.
Testing used swept (fixed or pulsed) sine
tones, and a selection of bass heavy music with
contrasting frequency content.
The vibration/acoustic setup and ‘tuning’
applied findings from my journal research. For
example, I used:
I refined these parameters through participant
feedback, and found that the ideal settings
accorded well with what was suggested through
other research.
The following test outcomes were the most
valuable to the ideas and methods I took to
sensation composition during the Masters
research.
Comparing modes of presentation
Using the vibration floor did not simply
replace the acoustic energy with a more direct
sensation interface. The qualities of sensation
were fundamentally different, being more
grounded in the body.
Overall, at most frequencies participants found
that they were more comfortable with vibration
energy than with the acoustic only system.
However, in the higher bass frequencies
acoustic and vibration energy became more
similar in sensation qualities.
Vibration sensation ‘bodily placement’
(localised sensation) did not correlate with
findings from the acoustic only system,
suggesting that the way the body is excited by
direct vibration is significantly different. Some
effects were specific to the vibration system,
such as a sense of the feet shaking. The range of
sensations experienced were broad, including
effects in the upper body, face, legs and back.
In most tests the acoustic only system was less
enjoyable for participants. Because the acoustic
energy did not involve the body as directly, low
frequency information was less tangible and
less defined.
Compared to the vibration floor setting,
the sound-only setting led to additional
reverberation of low frequency sound within
the space. This significantly ‘muddied’ the
overall sound experience.
Interesting perceptual responses to sensation
The testing suggested unique perceptual quirks
when people experience sensation as vibration.
Participants reported the sensation as moving
around the body with different frequencies,
skin sensation, a sense of vertigo and a
feeling of tiredness occurring with specific
frequencies, and perceptual placement of
frequencies within the room.
However, these responses were not consistent
between participants, and there were not
specific frequencies with predictable effects.
I suspected that testing in open spaces or
specially designed testing environments may
have provided more consistent results.
Participants engaging with the direct sensation
Most participants quickly found that they
became more involved with music when the
vibration floor was engaged. In addition to
compelling more attention to the music, the
floor itself became something to interact with
and was missed when deactivated.
Descriptions included: the floor creating a
nicer experience because sensation was more bodily, feeling more involved and consumed,
increased awareness of high frequency sound
(in its relationship to the sensation), increased
awareness of low frequency sound, quick
association with the vibration experience,
and that the floor created another level of
interaction or relationship.
Frequency
Each music test track had a different frequency
emphasis. Participants favoured pieces with
frequency content extending into the very low
frequencies (20-45 Hz), where the contribution
of the floor was felt to be more essential.
Tracks where frequency emphasis was centred
closer to the upper operating frequency of
the floor (~85Hz) still benefited. However,
vibration effects were noticed as ‘buzzing’ or
were perceived to be located in the floor, rather
than a logical extension of audible sounds.
This may have been partly due to the type of
technology used (modified loudspeakers rather
than dedicated vibration actuators).
Participants found that when the low frequency
information was distinctly different from
high frequency information, the floor failed
to enhance the music experience. Rather,
with auditory and vibration senses processing
separate information, the floor became a
distraction and could be disorientating due to
lack of cohesion.
This was primarily noticed on one track, which
had an atypical gap in information between
low and high frequencies. All other tracks
contained some degree of acoustic ‘artefacts’
in the upper harmonics of the predominant
(vibration sensed) bass information, which
possibly aided in tying sensory information
together.
Envelope
Participants favoured the vibration interface
in tracks where low frequency rhythm was
not overtly punctuated (i.e. having a rolling
or fuzzy quality). More punctuated rhythm
appeared to highlight differences between
acoustic and vibration information, perhaps
because the chronological space of definite
‘beats’ promoted more critical perceptual
processing.
This result was consistent with the findings of
William Martens on envelope and timing delay
tolerances.16
Dialogue between the senses
Feeling the bass as vibration sensation ‘muted’
auditory sensitivity to the complementary
sound. Most participants did not perceive
acoustic energy in the room until acoustic
levels were much higher than the normal
perceptual thresholds.
With sine tests, most of the participants
identified the same frequency point (56-57Hz)
where the energy shifted from vibration to
acoustic borne.
However, while this correlation was notable, I
suspected it was influenced by the specifics of
the testing room and audio setup. For example,
room modes and resonances, and the slightly
uneven frequency response of the loudspeakers
at the crossover points would have affected the
audio levels around the room, depending on
the frequency.
One participant identified a frequency where
they felt that their focus was flipping between
the vibration and acoustic system, at a point where both energies were perceived to be at
similar levels. This suggested that, although
there is some degree of perceptual blending
with combined vibration/acoustic energy, the
potential exists for sensory confusion when the
two sources of information are similar.
Similarly, tests with music tests tracks
suggested that vibration and acoustic
perception, although working together, can
compete with and affect each other, and this
effect is dependent on the frequency make-up
of each source. For example, the frequency
focus of the bassline, the transition from low
to high frequency content, and the type of
frequency gaps between the very low and midhigh
frequencies will all influence the results.
1. Griffin, M. J. (1990). Handbook of human vibration.
London ; San Diego, Calif., Academic Press.
2. Griffin, 1990; Verrillo, R. (1992). Vibration sensation in
humans. Music Perception 9(3): 281-302.
3. William Martens, personal correspondence.
4. Verrillo, 1992
5. Dalgarno, G. A vibroacoustic couch to improve
perception of music by deaf people and for general
therapeutic use. 6th International Conference on Music
Perception and Cognition. Aug 5th, 2000. Keele University
6. Altinsoy, E., Blauert, J., and Treier, C. (2001) Inter-
Modal Effects of Non-Simultaneous Stimulus Presentation,
Proceedings of the 17 th International Congress on
Acoustics. Rome, Italy
7. Daub, M., and Altinsoy, E. (2004). Audiotactile
simultaneity perception of whole-body vibrations
produced by musical presentations, in Proceedings of the
CFA/DAGA’04.
8. Martens, W. L. (2004). Perceived synchrony in a bimodal
display: optimal intermodal delay for coordinated auditory
and haptic reproduction. International conference on
auditory display, Sydney, Australia.
9. Martens, W. L. (2005). Tolerance for delay between
whole-body vibration and audio reproduction of musical
sound. Twelfth International Congress on Sound and
Vibration, Lisbon.
10. Martens, 2005.
11. Altinsoy, M. E. (2003). Effect of loudness on the haptic
force-feedback perception in virtual environments. Journal
of the Acoustical Society of America 114(4): 2330.
12. Hooper, J. (2002) Is VA therapy, music therapy?
Music Therapy Today (online), available at http://
musictherapyworld.net
13. Hooper, 2002
14. Dalgarno, 2000
15. Dalgarno, 2000
16. Martens, 2005